Tylenol. Advil. Monistat 7. Imodium AD. These are some of the most commonly used, widely available, and successful drugs in the United States. All of them began as drugs only available by a prescription. All of them made a successful prescription-only to over-the-counter (Rx-to-OTC) switch through the switch" mechanisms of the Food and Drug Administration (FDA). Due to the amount of money that pharmaceutical companies can make with an Rx-to-OTC switch, the FDA has received dozens of switch requests in the last few years, and it expects to receive many more in the near future.